(1) Field of the Invention
The present invention relates to a method of and device for automatically controlling a rotary wing aircraft having at least one propulsion propeller, to an autopilot device, and to an aircraft.
(2) Description of Related Art
The term “aircraft” includes in particular rotorcraft, i.e. aircraft provided with a rotary wing, and including helicopters.
For example, a helicopter comprises a rotary wing that includes at least one main rotor for providing the helicopter with propulsion and lift.
The longitudinal attitude and thus the pitching angle of the helicopter are then necessarily a function of the travel speed of the helicopter. At high speed, a helicopter thus presents a considerable pitching angle, and consequently a strongly nose-down longitudinal attitude.
It can be understood that at high speed, the helicopter presents a large nose-down aerodynamic angle of attack, which angle of attack generates penalizing aerodynamic drag.
It should be recalled that the longitudinal attitude of a rotorcraft represents the pitching angle of said rotorcraft, i.e. the angle between the reference longitudinal axis of the rotorcraft and the orthogonal projection of said longitudinal reference axis onto a plane normal to the gravity direction.
In contrast, the aerodynamic angle of attack of a rotorcraft represents the angle between the longitudinal reference axis of the rotorcraft and the orthogonal projection of the air speed vector of the rotorcraft onto a vertical plane containing said longitudinal axis.
Finally, the term “air-path slope” designates the angle of the air speed vector of said aircraft relative to its orthogonal projection onto a plane normal to the gravity direction.
Under such circumstances, the longitudinal attitude of a rotorcraft is equal to the algebraic sum of the angle of attack plus the air-path slope of the aircraft.
Furthermore, certain rotorcraft are also provided with at least one propulsion propeller.
It then becomes possible to adjust independently the longitudinal forward speed, the vertical speed, and the longitudinal attitude of such a rotorcraft.
It should be observed that the state of the art includes the document US 2011/0040431, and also the document US 2008/0237392 that describes a rotary wing aircraft having a propulsion propeller.
According to document US 2008/0237392, a subsystem of a control architecture provides vertical control and pitching control of the aircraft.
Document WO 99/50611 forms part of a state of the art that is remote from the invention, that document WO 99/50611 relating to a control and firing system.